multi: introduce new paymentsDB package

We introduce a new package paymentsDB and start by moving the
payment specifc errors from the channeldb package to the
paymentsDB package. We also fix linter issues which showed up
due to changing this code part.

lnrpc/routerrpc/router_server.go

@@ -22,6 +22,7 @@ import (
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/macaroons"
+	paymentsdb "github.com/lightningnetwork/lnd/payments/db"
 	"github.com/lightningnetwork/lnd/routing"
 	"github.com/lightningnetwork/lnd/routing/route"
 	"github.com/lightningnetwork/lnd/zpay32"
@@ -373,9 +374,9 @@ func (s *Server) SendPaymentV2(req *SendPaymentRequest,
 			payment.Identifier(), err)
 
 		// Transform user errors to grpc code.
-		if errors.Is(err, channeldb.ErrPaymentExists) ||
-			errors.Is(err, channeldb.ErrPaymentInFlight) ||
-			errors.Is(err, channeldb.ErrAlreadyPaid) {
+		if errors.Is(err, paymentsdb.ErrPaymentExists) ||
+			errors.Is(err, paymentsdb.ErrPaymentInFlight) ||
+			errors.Is(err, paymentsdb.ErrAlreadyPaid) {
 
 			return status.Error(
 				codes.AlreadyExists, err.Error(),
@@ -955,13 +956,13 @@ func (s *Server) SendToRouteV2(ctx context.Context,
 
 	// Transform user errors to grpc code.
 	switch {
-	case errors.Is(err, channeldb.ErrPaymentExists):
+	case errors.Is(err, paymentsdb.ErrPaymentExists):
 		fallthrough
 
-	case errors.Is(err, channeldb.ErrPaymentInFlight):
+	case errors.Is(err, paymentsdb.ErrPaymentInFlight):
 		fallthrough
 
-	case errors.Is(err, channeldb.ErrAlreadyPaid):
+	case errors.Is(err, paymentsdb.ErrAlreadyPaid):
 		return nil, status.Error(
 			codes.AlreadyExists, err.Error(),
 		)
@@ -1368,7 +1369,7 @@ func (s *Server) subscribePayment(identifier lntypes.Hash) (
 	sub, err := router.Tower.SubscribePayment(identifier)
 
 	switch {
-	case errors.Is(err, channeldb.ErrPaymentNotInitiated):
+	case errors.Is(err, paymentsdb.ErrPaymentNotInitiated):
 		return nil, status.Error(codes.NotFound, err.Error())
 
 	case err != nil: